This invention relates to improvements in apparatus for transferring objects and more particularly, it concerns an improved apron and drive mechanism for apparatus used principally to transfer non-ambulatory patients from a hospital bed or other surface on which they are initially reclined to a mobile carriage by which they may be supported and/or subsequently transferred to a second surface such as a surgical table, X-ray table or another bed.
The development of object or patient transferring apparatus of the type to which the present invention principally pertains is reflected in the disclosures of the following U.S. patents: No. 3,493,979 issued Feb. 10, 1970, to Laurel A. Koll and Walter Crook, Jr.; No. 3,579,672 issued May 25, 1971, to Laurel A. Koll and Walter Crook, Jr.; No. 3,765,037 issued October 16, 1973, to Albert Dunkin; and No. 3,829,915 issued Aug. 20, 1974, to Albert Dunkin. The apparatus particularly disclosed in the latter two of these patents has been commercialized and is currently found in many hospitals and similar institutions.
In essense, such apparatus includes, in addition to a load carrying mobile base or chassis, a pair of laterally translatable superposed, sheet-like apron supporting separator members about which a pair of upper and lower fabric-like aprons are trained. The aprons are established by very thin endless belts formed of fiberglass or nylon reinforced teflon and are independently controlled in a manner such that during lateral extension of the separators out over a bed and under a patient to be transferred, the respective flight portions of the upper and lower aprons which contact the patient and the bed remain relatively stationary and thus isolate both the patient and the bed from frictional contact with the laterally moving separator plates. When the patient is fully positioned on the assembly of aprons and separator plates, the condition of the upper apron is changed so that the upper flight portion thereof, in physical contact with the patient, will move in the same direction and at the same linear speed as the separator plates during retraction to transfer the patient from the bed or other surface on which he was initially reclined to the mobile chassis. The lower flight portion of the lower apron is fixed to the chassis of the apparatus so that it remains stationary with respect to the surface of the bed also during the retraction of the separator and apron assembly. Correspondingly, the lower flight portion of the upper apron slides relative to the upper flight portion of the lower apron with which it is in frictional contact. Such sliding motion between the aprons or belts is accommodated by the low friction characteristics of the reinforced teflon from which they are made and the generation of unwanted static electricity is avoided by impregnating one or both of the belts forming the aprons with a conductive material such as graphite.
Although the use of fabric-like coverings or aprons to isolate an object from frictional contact with a supporting member advanced laterally under the object was known prior to the development represented by the aforementioned U.S. patents, the basic apparatus disclosed particularly in No. 3,579,672 and No. 3,765,037 possesses several unique features which are believed to be the basis for its immediate acceptance in the patient transfer field. Foremost of these features is the universal flexibility of the apron and separator assembly by which this assembly may conform to the irregular and unpredictable contour of the human anatomy reclined on a yieldable surface such as a bed mattress. This feature, combined with the facility for retaining to one-half inch or less the thickness of the plate-like transfer assembly movable under the object or patient to be transferred, enables a combined "softness" and "thinness" which makes it difficult for a bedridden patient to feel the assembly moving beneath him, not to mention a total absence of discomfort. Secondly, the provision for changing the condition of the upper apron relative to its separator plate not only enables the lateral loaded retraction of the assembly of aprons and plates to effect the transfer of the object or patient back to the apparatus, but does so without in any way lifting the object or patient from the surface on which he is initially reclined and with which a patient identifies emotionally. This feature is enhanced further by the upper apron defining a continuous surface extending from beneath the patient to the remote side of the apparatus to which the patient is transferred. As a result, the transfer of a hospital patient can be effected without subjecting the patient to any measure of fear or other emotional disturbance normally associated with patient handling operations.
In the apron drive and control mechanism disclosed in U.S. Pat. No. 3,765,037 and embodied in the presently available commercial apparatus, required movement or non-movement of upper apron flight portions is achieved by an organization of loop pulling rollers and alternately actuated brake means operating on the endless belt forming the upper apron in synchronism with translation of the separator supporting the apron. Belt tracking is effected by a steering roll serving also as a component in one of the brakes. While this apron drive and control mechanism has proven in practice to be highly reliable in the operation of existing patient transfer machines and relatively maintanence-free, the drive and control mechanism itself contributes significantly to overall machine weight and manufacturing costs. While both of these factors constitute a deterrent to complete acceptance of an otherwise useful and effective patient transfer device, the problems associated with excessive weight are perhaps more critical because of effect on machine mobility and manueverability.